should be standard hard line threads. Very hard to line up and easy to strip, don't ask! Did yours also have square block to screw into, or just into cylinders? My GMC had line on outside of back plate, but have had some inside too. Biggest problem is the fancy bends orig had at ends before nut, can't make them in shop. On my outside ones, I got new blocks with the bolts with holes to cylinder, and my brake shop can now make hoses with common fittings. I had small hose made up and it allows you to move around easier to align the nuts. Try around you for a brake wholesaler/service shop. One in my area is great with parts and knowledge on old trucks, rarely lets me down. I figure if they don't have it, it's not made or sold anymore.
